Hi everyone, This is part 2 of online repair. This river combines the directory parent pointer work that I took over from Allison after she departed with a bunch of new online repair functionality that enables rebuilding of directory trees and correction of problems with the tree structure. As a consequence, this river needs closer review than the previous river. I've changed the ondisk format of the parent pointers to make it easier to correct the directory structure, but that required some alterations to the attr log intent items to support looking up xattrs by name and value. AFAICT this part is stable enough for review-- I've been running a few testvm host systems with parent pointers enabled for about 6 months, and haven't noticed any problems. With this part added, there's a dramatic drop in the number of uncorrectable directory fields reported by the fuzz test suite. --D
